This invention relates to methods for processing electron tubes and more specifically to vidicon tubes.
The operating life of a vidicon tube is largely determined by the life of the thermionic cathode. The cathode often fails because of poisoning by contaminants from the tube environment before the end of its normal lifetime. Some of the contaminants are released during the activation of the tube's cathode. The cathode initially has a coating of several carbonates, such as barium, calcium and strontium carbonates, in a binder. During the exhausting of the tube, the cathode is activated by first vaporizing the binder and then converting the carbonates to oxides by using heat from both the cathode filament and an external RF heater. During normal activation some of the binder material and other by-products of the cathode conversion are deposited on the surface of other electrodes within the tube. Later during normal operation of the tube, the contaminants on the electrode surfaces are released as gases when the electrodes are scanned with the electron beam. The cathode is then exposed to these gases resulting in the poisoning and shortening of the cathode's life.